Hi,
DS214play arrived today and 5 hours into the usual 'quick setup' for a complete numpty like me, I can confirm that you can definitely stream non supported media content directly to your ATV from the NAS. But it is not immediately apparent how.
Putting aside that actual setup of Video Station (on your mac) and DS Video (on your iphone) all I can do is reinforce Darkslide's comments on how to do this because it took me a fair few goes and a lot of swearing to get it right.
What you must do, is what Darkslide says. Don't do what I think is intuitive, which is to press the big play icon on the image of the video you have selected (on the detailed film information page he refers to), then go to the next screen (with the expected play/pause controls etc) then see the airplay icon on the right and click that. Doing this streams the movie to your phone and from your phone to the ATV as discussed above. You can test this by exiting the app and the playback stops. The same thing happens when following the same process on your mac.
But.... If you finally spot that there really is a *tiny* icon (and it's not an 'airplay' icon either) at the top right hand corner of the detailed movie information page and press this rather than the big play icon on the poster of the movie you want to play, then you will get a different screen with a play/stop control. If you get this, then you are streaming direct from the NAS to the ATV. As before, you can test this by switching off your phone and the playback continues.
I'm happily watching a .mkv being transcoded and streamed directly to my ATV as I type this.
Apologies if this seems to merely repeat what has been said previously, however I found this a really helpful thread in setting up my network and actually getting the DS214play to actually do 'what it says on the tin'. Thanks for all of your help.
Ben